In the Redux architecture, actions and reducers are foundational elements that facilitate the deterministic and predictable management of the application’s state. Together, they provide a structured way to describe and handle changes to the state.
Actions in Redux are plain JavaScript objects that represent information about an event or a change that should take place in the application. Every action must have a `type` property, which typically is a string constant that gives a clear, readable description of the event, like `’ADD_TODO’` or `’UPDATE_USER’`. Actions can also carry additional data required to process the event, often encapsulated within a `payload` property. For example, an action to add a to-do might look like `{ type: ‘ADD_TODO’, payload: { text: ‘Learn Redux’ } }`. Actions are dispatched in response to user interactions, API calls, or other events, signaling the intent to transform the state in a specific manner.
Reducers, on the other hand, are pure functions that determine how the application’s state should change in response to an action. A reducer takes in two arguments: the current state and an action. It then returns the next state based on the action’s type and, if applicable, its payload. Crucially, reducers do not modify the existing state; instead, they produce a new state object, ensuring the state’s immutability. For example, in response to the `’ADD_TODO’` action, a to-do reducer might return a new array of to-dos with the new item appended.
The beauty of reducers lies in their predictability. For any given state and action, a reducer will always produce the same output. This determinism makes state transitions transparent and testable.
While actions articulate “what happened” in a Redux application, reducers specify “how the state should change” in response. Their collaboration ensures a consistent and unidirectional flow of data, making state management in Redux applications systematic and maintainable.
